专题3静止图像编码标准英.pptVIP

Several typical image/video compression coding standard H.261、H.263:TV Conference and Visual Telephone System； JPEG、JPEG2000:Still Image Compression； MPEG-1: VCD； MPEG-2: DTV、DVD、HDTV； MPEG-4: Multimedia Communication。 JPEG standard JPEG (Joint Photographic Experts Group) Reducing the size of photographic images or continuous-tone artwork – pictures JPEG compression can be performed on 24-bit color or 8-bit grayscale images. JPEG Compression Arithmetic DCT: lossy compression Predictive coding : lossless compression JPEG image reconstruction mode： Sequential decoding (line-by-line) ； Progressive decoding (refinement of the whole image) Four different modes Lossy Sequential DCT based mode Baseline process that must be supported by every JPEG implementation. Expanded Lossy DCT based mode enhancements to baseline process Lossless mode low compression ratio allows perfect reconstruction of original image Hierarchical mode accomodate images of different resolutions JPEG coding system The baseline process The extended process Diagram of DCT encode and decode Original image data Rebuild image data DCT IDCT Quantizer Re-quantize Quantize table Entropy encode Entropy decode Code output channel 8×8 sub MB 8×8 sub MB f(x,y) f’(x,y) F(u,v) F’(u,v) S(u,v) Q(u,v) Q(u,v) JPEG standard give the brightness DCT coefficient quantization step JPEG standard give the chroma DCT coefficient quantization step Relative DCT coefficients The quantization coefficients The inverse quantization coefficients Rebuild image sub MB brightness value The baseline process Lossy Sequential DCT based mode DC components coding 8×8 block →DCT →DC coefficient DPCM Huffman coding AC components coding Zigzag scanning → Run-length coding Huffman coding Example： Diff=7，000000000111 100111， Diff=-7，111111111000 100000， Diff=3，000000000011 01111， Diff=-3，111111111100 01100